A mobile communication system that is studied as an evolved universal terrestrial radio access network (E-UTRAN) includes a mobile station 00 and a radio base station apparatus 10 as shown in FIG. 2.
Such a mobile communication system is configured to perform a contention-based random access procedure as shown in FIG. 1, by using a random access signal (contending-channel signal; Random access preamble) on the following occasions:
an occasion in which the mobile station 00 starts communications with the radio base station apparatus 10;
an occasion in which the mobile station 00 starts communications with a handover target cell; and
an occasion in which the mobile station 00 resumes communications with a cell to which the mobile station 00 is currently connected.
Here, such a random access procedure will be described with reference to FIG. 1 (refer to Non-patent Document 1).
As shown in FIG. 1, in step S101, a mobile station UE selects one random access preamble identifier among from a plurality of random access preamble identifiers, and transmits a random access preamble (RA-preamble) identified with the selected random access preamble identifier to a radio base station apparatus eNB.
In step S102, upon detecting one or multiple random access preambles transmitted by one or multiple mobile stations UE, the radio base station apparatus eNB transmits a random access response signal identifier (RA-RNTI: Random access radio network temporal identifier), which is used for identifying a random access response signal (contending-channel response signal; Random Access Response), to each of the one or multiple mobile stations UE, together with a random access response signal including at least the following information elements.
an RA-preamble identifier;
timing alignment information;
an uplink assigned resource (Initial UL grant); and
a temporary mobile station identifier (Temporary C-RNTI: cell specific radio network temporal identifier).
In step S103, upon receiving the random access response signal, the mobile station UE transmits an uplink signal by using the uplink resource assigned and indicated by the radio base station apparatus eNB.
In step 104, since there is a possibility that contention occurs between the multiple base stations UE when the random access signals (Random access preambles) are received, the radio base station apparatus eNB, which has received the uplink signals from the mobile stations UE, transmits a contention resolution signal (Contention resolution) to resolve the contention.
On the other hands, when transmitting the uplink signal, a mobile stations UE for which an uplink scrambling sequence is set transmits the uplink signal after performing scramble processing in which a scrambling sequence specific to the mobile station (UE specific scrambling sequence) is used (refer to Non-patent Document 2).
However, in a case where the mobile stations UE starts the random access procedure for any one of the following purposes, there is a problem that the mobile station UE cannot scramble an uplink signal in step 103, since the radio base station apparatus eNB would not be able to specify the mobile station transmitting the uplink signal in step 103 shown in FIG. 1:
the mobile station UE starts communications with the radio base station apparatus eNB;
the mobile station UE starts communications with a handover target cell; and
the mobile station UE resumes communications with a cell to which the mobile station UE is currently connected.
Additionally, in a case where the mobile station UE transmits an uplink signal in step 103 without performing scramble processing, there is a problem that uplink interference to neighboring cells increases.
Non-patent Document 1: 3GPP TS 36.300 Evolved universal terrestrial Radio access (E-UTRA) and E-UTRAN Overall description; Stage 2 (Release 8) V8.1.0
Non-patent Document 2: 3GPP TS 36.211 Physical channels and modulation (Release 8) V1.0.3